The Subnuclear Distribution of 5-HT1A Receptors in the Human Nucleus of the Solitary Tract and Selected Structures of the Caudal Medulla

The distribution of 5-HT1A receptors in the subnuclei of the human caudal nucleus of solitary tract and adjacent structures in the dorsal vagal complex was studied using [3H]8-OH-DPAT, a highly selective 5-HT1A receptor agonist. The highest binding of the labeled ligand was found in the dorsal motor nucleus of the vagus, followed by the medial, intermediate, and subpostremal subnuclei of the nucleus of solitary tract. Previous animal studies suggest an important role for these structures in the regulation of visceral function, particularly for the gastrointestinal and cardiovascular systems. The results of this study suggest the possibility of an analogous role for 5-HT1A receptors in the regulation of these autonomic pathways in humans as well.

Circadian clock genes and respiratory neuroplasticity genes oscillate in the phrenic motor system

Circadian rhythms are endogenous and entrainable daily patterns of physiology and behavior. Molecular mechanisms underlie circadian rhythms, characterized by an ~24-h pattern of gene expression of core clock genes. Although it has long been known that breathing exhibits circadian rhythms, little is known concerning clock gene expression in any element of the neuromuscular system controlling breathing. Furthermore, we know little concerning gene expression necessary for specific respiratory functions, such as phrenic motor plasticity. Thus, we tested the hypotheses that transcripts for clock genes ( Bmal1, Clock, Per1, and Per2) and molecules necessary for phrenic motor plasticity ( Htr2a, Htr2b, Bdnf, and Ntrk2) oscillate in regions critical for phrenic/diaphragm motor function via RT-PCR. Tissues were collected from male Sprague-Dawley rats entrained to a 12-h light-dark cycle at 4 zeitgeber times (ZT; n = 8 rats/group): ZT5, ZT11, ZT17, and ZT23; ZT0 = lights on. Here, we demonstrate that 1) circadian clock genes ( Bmal1, Clock, Per1, and Per2) oscillate in regions critical for phrenic/diaphragm function, including the caudal medulla, ventral C3–C5 cervical spinal cord, and diaphragm; 2) the clock protein BMAL1 is localized within CtB-labeled phrenic motor neurons; 3) genes necessary for intermittent hypoxia-induced phrenic/diaphragm motor plasticity ( Htr2b and Bdnf) oscillate in the caudal medulla and ventral C3–C5 spinal cord; and 4) there is higher intensity of immunofluorescent BDNF protein within phrenic motor neurons at ZT23 compared with ZT11 ( n = 11 rats/group). These results suggest local circadian clocks exist in the phrenic motor system and confirm the potential for local circadian regulation of neuroplasticity and other elements of the neural network controlling breathing.

Far-Lateral Approach for Medullary Cavernous Malformation: 2-Dimensional Operative Video

Medullary cavernous malformations are the rarest subtype of brainstem cavernous malformation and are associated with a high degree of morbidity. Selection of surgical candidates is critical, and cases are most favorable when the cavernous malformation abuts the surface of the brainstem. This limits the amount of native tissue transgressed during the resection. This patient had a large cavernous malformation within the caudal medulla eccentric. A right-sided paramedian far-lateral approach was used to access the brainstem. The cavernous malformation was readily apparent along the medullary surface and was dissected away in its entirety. Postoperative imaging confirmed complete resection. The patient gave informed consent for surgery and video recording. Institutional review board approval was deemed unnecessary. Used with permission from Barrow Neurological Institute, Phoenix, Arizona.

Connections between expiratory bulbospinal neurons and expiratory motoneurons in thoracic and upper lumbar segments of the spinal cord

Cross-correlation of neural discharges was used to investigate the connections between expiratory bulbospinal neurons (EBSNs) in the caudal medulla and expiratory motoneurons innervating thoracic and abdominal muscles in anesthetized cats. Peaks were seen in the cross-correlation histograms for around half of the EBSN-nerve pairs for the following: at T8, the nerve branches innervating internal intercostal muscle and external abdominal oblique muscle and a more distal branch of the internal intercostal nerve; and at L1, a nerve branch innervating internal abdominal oblique muscle and a more distal branch of the ventral ramus. Fewer peaks were seen for the L1 nerve innervating external abdominal oblique, but a paucity of presumed α-motoneuron discharges could explain the rarity of the peaks in this instance. Taking into account individual EBSN conduction times to T8 and to L1, as well as peripheral conduction times, nearly all of the peaks were interpreted as representing monosynaptic connections. Individual EBSNs showed connections at both T8 and L1, but without any discernible pattern. The overall strength of the monosynaptic connection from EBSNs at L1 was found to be very similar to that at T8, which was previously argued to be substantial and responsible for the temporal patterns of expiratory motoneuron discharges. However, we argue that other inputs are required to create the stereotyped spatial patterns of discharges in the thoracic and abdominal musculature.